Optical arrangement for high speed printout system

ABSTRACT

A printing system including a photoconductive surface having a charge placed over an area of the surface. An optical means for selectively discharging portions of that area is employed to form a charge and discharge portion representative of an electrostatic latent image. The optical means includes an array of light emitting solid state devices with appropriate logic circuitry for selectively energizing certain elements of the array in order to form the electrostatic latent image. In order to position the light images in a line and more closely together than their respective sources, the light emitting sources are placed in two parallel linear arrays. The images of each linear array are combined by projection through a bi-prism to effect a single linear array of closely packed light images.

United States Patent [191 Mailloux m 3,827,062 [451 July 30, 1974 OPTICAL ARRANGEMENT FOR HIGH SPEED PRINTOUT SYSTEM [75] Inventor: Louis D. Mailloux, Fairport, NY. [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Dec. 18, 1972 [21] Appl. No.: 316,187

[52] US. Cl 95/4.5 R [51] Int. Cl B4lb 21/24 [58] Field of Search 95/4.5 R; 340/378 [56] References Cited UNITED STATES PATENTS 3,007,380 ll/l96l Ketz 95/45 3,286,585 ll/l966 McCullough 95/4.5

Primary Examiner-John M. Horan [5 7 ABSTRACT A printing system including a photoconductive surface having a charge placed over an area of the surface. An optical means for selectively discharging portions of that area is employed to form a charge and discharge portion representative of an electrostatic latent image. The optical means includes an array of light emitting solid state devices with appropriate logic circuitry for selectively energizing certain elements of the array in order to form the electrostatic latent image In order to position the light images in a line and more closely together than their respective sources, the light emitting sources are placed in two parallel linear arrays. The images of each linear array are combined by projection through a bi-prism to effect a single linear array of closely packed light images.

4 Claims, 4 Drawing Figures PATENTEDJ L HH 3.827. 062

sum 1 or 2 OPTICAL ARRANGEMENT FOR HIGH SPEED PRINTOUT SYSTEM BACKGROUND OF THE INVENTION This invention relates to printing devices and more particularly to an improved device for optically forming images on a photoreceptive surface.

The operation of a communication printer relies upon the appearance of an electrical signal input corresponding to information to be printed which is converted into an appropriate alphanumeric or other representation which is printed on a suitable support surface such as copy paper or the like. The present invention is applicable for use in a printing device which responds to pluralities of information input signals received in electrical form and which are translated into optical images and in turn employed in conjunction with a xerographic reproduction process employing electrostatic imaging or the like.

The printing apparatus in which the present invention may be used is more fully described in copending application Ser. No. 292,029, filed Sept. 25, I972, by S. W. Ing and J. F. Stephany. As described therein, the electrical signals are converted to optical signals by light emitting diodes in a linear array. For general application in a xerographic process, a linear array of such diodes must have at least a thousand elements evenly spaced across an 8 inch width. There is a practical limit to the density with which such a linear array of light emitting diodes can be placed because of inherent physical structure of the diode. For the sake of description it may be considered that each light emitting element includes a cladding, thus resulting in an inherent spacing between light sources. This operates as a limitation on the bit density obtainable from a linear array of diodes.

SUMMARY OF THE INVENTION It is an object of this invention to provide an optical system to increase the bit density obtainable from an array of light sources.

Briefly, this invention is practiced in one form by a pair of parallel linear arrays of light emitting diodes, the two lines being longitudinally offset relative to each other by approximately the diameter of a single light emitting diode. The images of these parallel linear arrays of light sources are made to overlap in a single image line by projection through a pair of symmetrically disposed prisms which refract the propagating images to positions along a common image locus.

For a better understanding of this invention, reference is made to the following detailed description of the invention given in connection with the accompanying drawings.

DRAWINGS FIG. 1 is a somewhat schematic representation of a plurality of light sources directing light onto a photoconductive surface.

FIG. 2 is a representation of the manner in which a linear array of light emitting solid state devices forms an alphanumeric character upon a photoreceptive surface in a line by line fashion.

FIG. 3 is an optical diagram of the arrangement shown in FIG. 1 and including an optical system according to the present invention.

FIG. 4 is a representation of two rows of light sources and their aligned images.

DESCRIPTION Referring now to FIG. 1, a photoreceptive or xerographic surface is shown at 2 and is mounted for rotation on a drum 4. A linear array of light emitting diodes is shown at 6 and is made up of a plurality of individual segments 8 which are in turn composed of a plurality of individual light emitting diodes 10.

A projection lens 12 is disposed between the diode linear array 6 and the photoreceptive surface 2. Light from each individual diode source 10 propagates along an optical axis represented at 14 and is imaged by the projection lens 12 on the photoreceptive surface 2.

FIG. 2 shows how the formation of an alpha-numeric, graphic, or pictorial symbol is accomplished by a matrixing arrangement. As illustrated in FIG. 2, an array of light emitting diodes 6 is positioned relative to the photoreceptor 2 as if viewed from the right in FIG. 1. The photoreceptor 2 has a motion relative to the diode array 6 in the direction indicated by the arrow. The diode array 6 traverses the photoconductive surface 2 and selectively discharges the surface by imposition of a light beam at an appropriate spot. As shown in FIG. 2, the character 5 is defined on the photoreceptive surface character width of line diode spot formations and a character length or height of 7 diode spot formations. As the surface 2 moves relative to the diode array 6, the character 5 is formed by appropriately pusling individual diodes 10 in the first array segment 8 in a predetermined sequence. A first spot combination is pulsed at the first scanning line, a second spot combination pulsed at the second scanning line, a third spot combination at the third scanning line, and so on. In other words, as the surface 2 moves beneath the diode array 6, a portion of the segment 8 is energized to form the discharge area or spot positions in the first line. For forming the character 5 as shown, all five diodes 10 are energized at the first line. At the second scanning line, only the first diode 10 is energized. During the third scanning line, the first four diodes are energized, and so on until a completed character is formed. Of course, the other segments 8 may also be selectively energized at the same line time to provide character generation across the width of the document.

FIG. 2 is also illustrative that there is an inherent limit to the closeness or density with which the image points can be placed, because of the physical size, how ever small, of individual diodes 10.

Referring now to FIG. 3, the photoreceptive surface 2 and supporting drum 4 are again shown in relationship to the projection lens 12 and optical axis 14. A pair of diode linear arrays 6A and 6B are positioned at different positions offset from and relative to the optical axis 14. Preferably, the arrays 6A and 6B are located equidistant above and below the optical axis 14.

A prism, generally indicated at 16, is disposed along the optical axis 14 between projection lens 12 and photoreceptor 2. Prism 16 for the purpose of this invention acts as a pair of prisms l8 and 20, with their interface at the optical axis 14. It is immaterial whether prisms 18 and 20 are indeed separate prisms cemented at their interface on the optical axis 14 or whether they are in fact a single prism.

It will be apparent that without the interposition of prism 16 in this system, the diode arrays 6A and 6B would be imaged at the locations designated respectively 6A and 6B on the image plane 3. However, the prism 18 refracts the light propagating along the projection axis 22 from the array 68 so as to locate its image at image line 24 on the photoreceptor. Likewise, prism 20 refracts the light propagating along the projection axis 26 from diode array 6A to project its image at the same image point or line 24 on the photoreceptor 2. Image line 24 intersects the optical axis 14.

Referring now to FIG. 4, diode arrays 6A and 6B are shown and include a plurality of diode segments 8A and 88 respectively, these in turn consisting of a plurality of individual diodes 10. The images of individual diodes on rows 6A and 6B are shown aligned in image line 24. That is, the locus of the images of all sources is a line 24. Individual diodes 10 in the respective rows 6A and6B are laterally offset with respect to each other by the approximate diameter of the light bundle emitted from each diode. Accordingly, the image line 24 has a more densely packed linear array of light images than their respective sources. The phantom lines in FIG. 4 simply connect object or source light with respective light images to indicate that alternate spots on the image line 24 are derived from top and bottom linear arrays 6A and 68 respectively.

The light sources 10 in this arrangement are essentially monochromatic and therefore dispersion which would adversely affect a system such as this with ordinary light sources is not a factor here.

The foregoing description of an embodiment of this invention is given by way of illustration and not a limitation. The concept and scope of the invention are limited only by the following claims and equivalents thereof which may occur to others skilled in the art.

What is claimed is:

1. Optical apparatus for aligning the images of a plurality of offset spot sources of light for character generation by the selective on-off condition of said spot sources resulting in corresponding selective spot imaging, including:

a plurality of substantially monochromatic spot sources of light spaced from each other and spaced relative to an optical axis,

a projection lens disposed along said optical axis between said spot sources and an image plane for projecting images of said spot sources on said image plane, each such projection being along an individual projection axis corresponding to a single spot source,

refraction means disposed between said spot sources and said image plane to refract said projection axes and direct all of said projection axes to a common image line, whereby said images are aligned in a single linear array, free of chromatic aberration. 2. Optical apparatus for aligning the images of a plurality of offset spot sources of light for character generation by the selective on-off condition of said spot sources resulting in corresponding selective spot imaging, including:

a plurality of substantially monochromatic spot sources of light which are aligned in parallel linear arrays on opposite sides of an optical axis and equally spaced therefrom,

a projection lens disposed along said optical axis between said spot sources and an image plane for projecting images of said spot sources on said image plane, each such projection being along an individual projection axis corresponding to a single spot source of light,

a prism means disposed between said light sources and said image plane to refract said projection axes and direct the same to a common image line, whereby said images are aligned in a single linear array, free of chromatic aberration.

3. Optical apparatus as defined in claim 2 in which each of said spot sources is longitudinally displaced relative to the next by substantially the pupil of a single spot source.

4. A pair of parallel linear arrays of substantially monochromatic spot sources of light disposed equidistant from an optical axis extending perpendicularly to said linear arrays,

each of said linear arrays being displaced along its linear axis relative to the other by substantially half the distance between centers of individual spot sources,

a projection lens disposed along said optical axis between said spot sources and an image plane for projecting images of said spot sources on said image plane for character generation by the selective onoff condition of said spot sources resulting in corresponding selective spot imaging,

prism means disposed between said spot sources and said image plane to refract light propagating therebetween so that images of said linear arrays lie on a common image line,

whereby the images of said spot sources are aligned in a higher density array than the light sources themselves, free of chromatic aberration. 

1. Optical apparatus for aligning the images of a plurality of offset spot sources of light for character generation by the selective on-off condition of said spot sources resulting in corresponding selective spot imaging, including: a plurality of substantially monochromatic spot sources of light spaced from each other and spaced relative to an optical axis, a projection lens disposed along said optical axis between said spot sources and an image plane for projecting images of said spot sources on said image plane, each such projection being along an individual projection axis corresponding to a single spot source, refraction means disposed between said spot sources and said image plane to refract said projection axes and direct all of said projection axes to a common image line, whereby said images are aligned in a single linear array, free of chromatic aberration.
 2. Optical apparatus for aligning the images of a plurality of offset spot sources of light for character generation by the selective on-off condition of said spot sources resulting in corresponding selective spot imaging, including: a plurality of substantially monochromatic spot sources of light which are aligned in parallel linear arrays on opposite sides of an optical axis and equally spaced therefrom, a projection lens disposed along said optical axis between said spot sources and an image plane for projecting images of said spot sources on said image plane, each such projection being along an individual projection axis corresponding to a single spot source of light, a prism means disposed between said light sources and said image plane to refract said projection axes and direct the same to a common image line, whereby said images are aligned in a single linear array, free of chromatic aberration.
 3. Optical apparatus as defined in claim 2 in which each of said spot sources is longitudinally displaced relative to the next by substantially the pupil of a single spot source.
 4. A pair of parallel linear arrays of substantially monochromatic spot sources of light disposed equidistant from an optical axis extending perpendicularly to said linear arrays, each of said linear arrays being displaced along its linear axis relative to the other by substantially half the distance between centers of individual spot sources, a projection lens disposed along said optical aXis between said spot sources and an image plane for projecting images of said spot sources on said image plane for character generation by the selective on-off condition of said spot sources resulting in corresponding selective spot imaging, prism means disposed between said spot sources and said image plane to refract light propagating therebetween so that images of said linear arrays lie on a common image line, whereby the images of said spot sources are aligned in a higher density array than the light sources themselves, free of chromatic aberration. 